Briefly touched on in a recent discussion elsewhere:
Indonesian aircraft missing off Jakarta
As has been mentioned, transport aircraft that are optimized to maximize L/D are designed to fly with a small, positive pitch attitude. To design an airplane to fly with deck angle of exactly zero in cruise would be to leave unrealized performance on the table! Separately, optimization of takeoff, landing, and ground operations usually results in a slightly negative deck angle when taxiing. I strongly doubt that any commercial transport airplane has ever been designed to have exactly zero deck angle either during ground taxi or cruise.